Apparatus for marine seismographic prospecting

ABSTRACT

Apparatus for marine seismographic prospecting consists of a boom and a movable charge carrier attached to the boom. Using this apparatus an explosive charge may be submerged and towed at a constant, predetermined depth behind the ship.

United States Patent 775,028, Nov. 12, 1968, now abandoned.

APPARATUS FOR MARINE SEISMOGRAPHIC PROSPECTING U.S. Patent Office, class schedule class 198, conveyers, Power-Driven, 1956 Rev.

Primary Examiner-Rodney D. Bennett, Jr. Assistant Examiner-Daniel C. Kaufman Attorney- Cushman, Darby and Cushman ABSTRACT: Apparatus for marine seismographic prospecting consists of a boom and a movable charge carrier attached Using this apparatus an explosive charge may be submerged and towed at a constant, predetermined depth behind the ship.

13 Claims, 6 Drawing Figs.

U.S. Cl. ..l8l/0.5 VM, 18 110.5 XC Int. Cl 601v l/04,

G0 lv 1/38 to the boom. Field 01 Search 181/0.5 VM, 0.5 XC

APPARATUS FOR MARINE SEISMOGRAPHIC PROSPECTING This is a continuation of application, Ser. No. 775,028, filed Nov. 12, 1968, now abandoned.

This invention relates i an apparatus for submerging an explosive charge in marine seismographic prospecting operations and to a method of marine seismographic prospecting employing such apparatus.

In marine seismographic prospecting a charge of blasting explosive primed with a detonator is attached to a hook on the trailing end of flexible firing cable towed behind a moving ship and fired, successive charges being fired at predetermined intervals. It has been found that better seismograph records are obtained if an elongated explosive charge is fired under a depth of about 30 feet of water and in order to position the charge at this depth, a heavy cable or a weighted cable has been used. It has, however, proved extremely difficult to ensure that consecutive charges are fired at constant depth because of the effect of the ship speed and water surges on the cable depth. This effect is enhanced with elongated explosive charges such as lengths of detonating fusecord.

It is an object of this invention to provide means whereby an explosive charge may be submerged and towed at constant predetermined depth behind'a ship in marine seismographic prospecting operations.

In accordance with the invention an apparatus for submerging an explosive charge for marine seismographic prospecting comprises a boom adapted for attachment to a ship with its lower end submerged and its upper end adjacent to the ship's deck and a movable charge carrier attached to the boom, said carrier being movable longitudinally with respect to said boom from a position adjacent to the ships deck to a predetermined submerged position when the boom is attached to a ship in its operative position.

The boom is advantageously pivoted on the ship to facilitate its rotation to a position substantially parallel to the ships deck when the boom is not in use.

The charge carrier may advantageously comprise a movable band or rope trained around pulleys mounted on the boom, the charge being advantageously connected to the band or rope by a connector, for example a clamp formed with an eyehole. An endless band or rope is advantageous since this may be continuously rotated in one direction and may have a plurality of connectors at convenient positions along its length to which several charges may be attached. A high firing rate may thereby be achieved by, for example, arranging the charge connectors so that one is at a loading station on the deck whilst another with a charge attached is in a submerged position for holding a charge in position for firing.

The charge carrier alternatively comprise an elongated screw and longitudinally movable nut mounted thereon, the nut being provided with means to attach the charge thereto.

The apparatus may, if desired, further comprise an electric conductor which, when the boom is in its operative submerged position, has one end submerged and one end accessible at the ships deck for attachment of a firing energy source, the submerged end being adapted to connect electrically with an electric detonator in the explosive charge when the charge is lowered to the firing position.

The invention also includes a ship fitted with the aforedescribed apparatus.

In accordance with a further aspect of the invention a method of producing a record of underwater rock formations comprises attaching an explosive charge to a movable carrier mounted on a boom suspended from a ship with its lower end submerged, moving the carrier and charge to a predetermined submerged position, firing the explosive charge and recording the resulting seismic waves after reflection or refraction from underwater rock layer interfaces.

Further features of the invention are included in the embodiment which is hereinafter described, by way of example only, with reference to the accompanying drawings wherein FIG. 1 shows diagrammatically in elevation an apparatus mounted in operative position on a ship with an explosive charge attached;

FIG. 2 is a fragmentary detail of the apparatus of FIG. 1 shown in perspective;

FIG. 3 shows a fragmentary end view of the deck end of the assembly of FIG. 1;

FIG. 4 shows a diagrammatical elevation of a modification of the assembly of FIG. 1;

FIG. 5 shows on a larger scale a diagrammatic fragmentary section of the apparatus of FIG. 4 on the line V-V.

FIG. 6 is a fragmentary detail view showing a further modification of a charge carrier.

In the drawings like numbers refer to corresponding parts.

In the assembly shown in FIGS. 1, 2 and 3, a tubular metal boom 10 is mounted on a ship 11 by means of a journal 12 supported in a bearing 13 on a bracket 14 fixed to the ships bulwark. The lower end of the boom 10 is supported by straining ropes 15 which, when the ship is moving with the boom in the position shown, prevent excessive flexing of the boom. When not in use the boom may be rotated around the journal 12 to a position parallel to the ships deck. Pulleys l6 and 17 are mounted respectively at the upper and lower ends of the boom and a rope 18 is trailed around the pulleys. Pulley 16 is fitted with a handle to facilitate rotation of the pulleys and rope 18. A metal towing bracket 19 (FIG. 2) clamped on the rope 18, has an eyehole 20 which facilitates the attachment of an explosive charge by means of a hooked coupling. A stop contact 21 is mounted on bracket 22 on the lower end of the boom 10 but is insulated therefrom by a layer of electrically insulating material 23. The contact 21 is coupled to an electrical energy source 24 by a conductor cable 25.

In operation the boom is rotated to a position as shown in FIG. 1, the rope 18 is rotated to bring the bracket 19 to deck working level, an explosive charge 26, primed with an electric detonator 27, is coupled to the bracket 19 by means of a connector 28 and a metal tie rod 29. One electrical conductor wire 30 of detonator 27 is electrically connected to the tie rod 29 whilst the other wire 31, which is bare at its free end, remains free to trail in the water when submerged. The charge 26, which is illustrated as a detonating cord charge, is thrown overboard and the bracket 19 is lowered until it engages contact 21. The charge is now in position for firing, the electrical circuit comprising energy source 24, cable 25, contact 21, tie I rod 29, conductors 30 and 31 and earth return to the ship. After the charge is tired the bracket is raised to deck level and a further charge is affixed.

In the modification of the apparatus shown in FIGS. 4 and 5 the pulley 17 is a metal pulley mounted on a metal axle 32 attached to a bracket 33 of electrically insulating material, fixed on the end of the boom 10. The cable 25 is electrically connected to the axle 32. Part of bracket 22 and the contact 21 have been removed and electrical contact between the bracket 19 and the cable 25 is established through the pulley 17. Several brackets 19 are clamped on the rope 18, and the rope 18 may be moved in the same direction to bring simultaneously one bracket 19 to a firing position where it is in contact with pulley 17 and a further bracket 19 to the deck level where an explosive charge may be attached.

In the modification shown in FIG. 6 the charge carrier comprises an elongated screw 34 and a longitudinally movable nut 36 mounted thereon, the nut being provided with a towing bracket 19' having an eyehole 20' for facilitating the attachment of an explosive charge by means of a hooked coupling.

Iclaim:

l. A method of producing a record of underwater rock for mations, which comprises attaching an explosive charge to a movable carrier mounted on a rigid boom suspended from a ship with its lower end submerged, positively driving the carrier and charge to a predetermined submerged position, moving the ship forwardly through the water while preventing movement of the boom under the force of the water thereon, firing the explosive charge and recording the resulting seismic waves reflected or refracted from underwater rock layer interfaces.

2. An apparatus for submerging an explosive charge for marine seismographic prospecting comprising a rigid boom adapted for attachment to a ship with its lower end submerged and its upper end adjacent to the ship's deck, a movable charge carrier attached to the boom for longitudinal movement with respect to said boom from a position adjacent to the ships deck to a predetermined submerged position when the boom is attached to a ship in its operative position, drive means mechanically connected to said carrier for applying a positive driving force to said carrier in a direction longitudinally outwardly of said boom for effecting submergence of the charge, and means for preventing movement of said boom relative to the ship when said boom is in its operative position.

3. An apparatus as claimed in claim 2 wherein the charge carrier comprises an endless movable band or rope trained around pulleys mounted on the boom.

4. An apparatus as claimed in claim 3 wherein the band or rope is provided with at least one connector for attachment to the charge.

5. An apparatus as claimed in claim 4 wherein the connector comprises a clamp formed with an eyehole.

6. An apparatus as claimed in claim 3 wherein the endless band or rope may be continuously rotated in one direction.

7. An apparatus as claimed in claim 6 wherein the endless band or rope has a plurality of connectors.

8. An apparatus as claimed in claim 7 wherein the connectors are arranged on the endless band or rope so that one connector may be at a loading station on the ship's deck whilst another is in a submerged position for holding a charge in position for firing.

9. An apparatus as claimed in claim 2 wherein the charge carrier comprises an elongated screw having a longitudinally movable nut mounted thereon, the nut being provided with means for attachment of an explosive charge.

10. An apparatus as claimed in claim 2 further comprising an electric conductor which, when the boom is in its operative submerged position, has one end submerged and one end accessible at the ships deck for attachment of a firing energy source, the submerged end being adapted to connect electrically with an electric detonator in the explosive charge when the charge is lowered to the firing position.

11. A ship fitted with an apparatus as claimed in claim 2.

12. An apparatus as claimed in claim 2 wherein the boom is pivoted on the ship to facilitate its rotation to a position substantially parallel to the ships deck when it is not in use, and wherein said means for preventing relative movement of said boom prevents rotation of said boom in a direction opposite to the direction of ship travel.

13. Apparatus as in claim 12 wherein said means preventing relative movement of said boom includes means for connecting the lower part of said boom to the ship at a location forward of the pivot connection between said boom and the ship. 

1. A method of producing a record of underwater rock formations, which comprises attaching an explosive charge to a movable carrier mounted on a rigid boom suspended from a ship with its lower end submerged, positively driving the carrier and charge to a predetermined submerged position, moving the ship forwardly through the water while preventing movement of the boom under the force of the water thereon, firing the explosive charge and recording the resulting seismic waves reflected or refracted from underwater rock layer interfaces.
 2. An apparatus for submerging an explosive charge for marine seismographic prospecting comprising a rigid boom adapted for attachment to a ship with its lower end submerged and its upper end adjacent to the ship''s deck, a movable charge carrier attached to the boom for longitudinal movement with respect to said boom from a position adjacent to the ship''s deck to a predetermined submerged position when the boom is attached to a ship in its operative position, drive means mechanically connected to said carrier for applying a positive driving force to said carrier in a direction longitudinally outwardly of said boom for effecting submergence of the charge, and means for preventing movement of said boom relative to the ship when said boom is in its operative position.
 3. An apparatus as claimed in claim 2 wherein the charge carrier comprises an endless movable band or rope trained around pulleys mounted on the boom.
 4. An apparatus as claimed in claim 3 wherein the band or rope is provided with at least one connector for attachment to the charge.
 5. An apparatus as claimed in claim 4 wherein the connector comprises a clamp formed with an eyehole.
 6. An apparatus as claimed in claim 3 wherein the endless band or rope may be continuously rotated in one direction.
 7. An apparatus as claimed in claim 6 wherein the endless band or rope has a plurality of connectors.
 8. An apparatus as claimed in claim 7 wherein the connectors are arranged on the endless band or rope so that one connector may be at a loading station on the ship''s deck whilst another is in a submerged position for holding a charge in position for firing.
 9. An apparatus as claimed in claim 2 wherein the charge carrier comprises an elongated screw having a longitudinally movable nut mounted thereon, the nut being provided with means for attachment of an explosive charge.
 10. An apparatus as claimed in claim 2 further comprising an electric conductor which, when the boom is in its operative submerged position, has one end submerged and one end accessible at the ship''s deck for attachment of a firing energy source, the submerged end being adapted to connect electrically with an electric detonator in the explosive charge when the charge is lowered to the firing position.
 11. A ship fitted with an apparatus as claimed in claim
 2. 12. An apparatus as claimed in claim 2 wherein the boom is pivoted on the ship to facilitate its rotation to a position substantially parallel to the ship''s deck when it is not in use, and wherein said means for preventing relative movement of said boom prevents rotation of said boom in a direction opposite to the direction of ship travel.
 13. Apparatus as in claim 12 wherein said means preventing relative movement of said boom includes means for connecting the Lower part of said boom to the ship at a location forward of the pivot connection between said boom and the ship. 